Blish:  This site is for selling and buying digital content. They sell e-books, but from what I can tell they are downloadable for a limited time.  That I don’t like.  They also offer photos, how-to guides, clipart, music, sound loops, video, design templates.  I have never bought from this site. If anyone has any info (good or bad) let me know.  Prices seem reasonable on the few e-books I looked at.

Ebook Mall:  This retailer has been around for quite a while.  They have a info page describing the various e-book formats and devices and another page that compares formats and devices. Ebook Mall used to be rather expensive back in the Gemstar days, but now their prices are more in sync with other sites.

eScholarship Editions:   Site has close to 2000 books from academic presses and covers a range of topics, including art, science, history, music, religion, and fiction.  Select books are available to the public.

Bartleby:  Site offers contemporary and classic reference works. Good for students and researchers. Also they have 20 volumes of the Harvard Classics in Adobe, Microsoft, and Aportis formats.